Artificial eye and measuring instrument for measuring the  accommodation of an eye

ABSTRACT

A liquid lens system comprises a liquid drop 10 whose shape can be influenced by electrical fields. A plurality of electrodes are arranged annularly around the liquid drop. The liquid lens system may be employed in an artificial eye, an accommodation measuring instrument and a dioptric telescope.

CROSS REFERENCE

This application was originally filed as Patent Cooperation TreatyApplication Number PCT/EP2006/006028 filed Jun. 22, 2006, which claimspriority of European Application Number 05014074.8, filed Jun. 29, 2005.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a United States national phase application ofco-pending international patent application number PCT/EP2006/006028,filed Jun. 22, 2006, the disclosure of which is incorporated herein byreference.

BACKGROUND

The invention relates to an artificial eye and to a measuring instrumentfor measuring the accommodation of an eye, having a liquid lens system.

The prior art (products from Varioptic and Philips; U.S. Pat. No.6,369,954 and EP 1 019 758) discloses controllable liquid lenses, withwhich the refractive power can be controlled in the range of about −15dpt to 30 dpt within time intervals of a few milliseconds with voltagesof up to 100 V.

JP 011 40 118 describes a lens whose surface is formed by a resilientwall, which can be deformed by modification of electrical voltages.

SUMMARY

It is an object of the invention to provide an artificial eye with whichcomprehensive and informative measurements can be carried out for thepurpose of comparison with measurement on eyes in vivo.

To this end the invention provides an artificial eye having the featuresof patent claim 1. Advantageous configurations of the artificial eye aredescribed in the claims dependent on claim 1.

Another configuration of the artificial eye provides an adjustable pupilin the beam path between the said lenses.

According to another configuration, in order to improve the measurementresults and in particular to obtain reproducible measurement resultsunder varying conditions, the artificial eye is equipped with a laserbeam source for generating a beam comprising a multiplicity of parallellight rays, a CCD camera for recording images generated by the lightrays after they pass through the lenses, and with a computer forprocessing the images and for controlling the liquid lens system as afunction of the image processing.

The invention furthermore provides a measuring instrument for measuringthe accommodation of an eye, having a liquid lens system which comprisestwo liquid lenses with the features of claim 4.

A preferred configuration of this measuring instrument provides adisplay screen for representing an image, which is formed on the retinaof the eye. Another configuration of the measuring instrument provides acomputer for controlling the representation of the image so that theimage size and/or the brightness of the image represented on the displayscreen is/are adapted so that the brightness and size of the image onthe retina is independent of the visual defect to be examined. For apatient who sees sharply at a longer distance, for example, a point mustbe adjusted more brightly than for a patient who sees sharply in thenear field.

Lastly, another configuration of the measuring instrument provides twoliquid lens systems and a computer, which drives one liquid lens systemfor a spherical correction whereas it drives the other liquid lenssystem for a cylinder correction.

A liquid lens system of the type mentioned above may furthermore be usedadvantageously in a dioptric telescope. Such a dioptric telescopecontains preferably a liquid lens system for adjusting a refractivepower and preferably a liquid lens system for adjusting a cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be explained in more detail below with theaid of the drawing, in which:

FIG. 1 schematically shows a section through a liquid lens system;

FIG. 2 schematically shows a plan view of the electrode arrangement of aliquid lens system according to FIG. 1;

FIG. 3 shows an artificial eye;

FIG. 4 shows a metrological layout of an artificial eye according toFIG. 3;

FIG. 5 shows an accommodation measuring instrument; and

FIG. 6 shows a dioptric telescope.

DETAILED DESCRIPTION

According to FIG. 1 a liquid drop 10, in the exemplary embodimentrepresented an oil drop, is arranged between two radiation-transparentwindows 12, 14. Radiation (light) to be imaged is refracted by theliquid drop 10 in an adjustable way.

The liquid drop 10 rests on a transparent interlayer 18, which is inturn supported by a support ring 16.

An electrode ring 20, which is represented in a plan view in FIG. 2, isarranged around the liquid drop 10. As shown by FIG. 2, the electrodering 20 in the exemplary embodiment represented consists of eightsegments (20 a, 20 b, 20 c, 20 d, 20 e, 20 f, 20 g, 20 h). The saidsegments form a closed circle. FIG. 2 also shows the electrical voltagesU1, U2, U3, U4, U5, U6, U7 and U8 which can selectively be appliedrespectively to the individual segments. By applying different voltagesto the individual segments, the surface 26 of the liquid drop 10 can bemodified so that the refractive properties of the liquid drop 10 areselectively adjustable. A ring 28 forms an e.g. “earthed” back electrodefor the individual electrodes 20 a, . . . , 20 h. In order to replicatea cylinder lens, for example, the voltages U2, U3, U6, U7 must be set toa first voltage potential and the voltages U1, U4, U5, U8 of the othersegments must be set to a different voltage potential. In this way, alens defect can be set up electrically with a liquid lens systemaccording to FIGS. 1 and 2, for example a sphere, a cylinder, coma orother defects of higher order. The more segments there are arrangedaround the liquid drop 10 similarly as in FIG. 2, the higher is thespatial resolution of the lens defects which can be adjusted. Thearrangement of the individual electrode segments (20 a, . . . , 20 h)need not necessarily be rotationally symmetric. The exemplary embodimentaccording to FIG. 2 actually shows an eight-fold rotational symmetry ofthe electrodes, so that two electrodes in each case lie diametrically inrelation to the liquid drop 10. As a variant of this exemplaryembodiment, particularly in order to generate aspherical deformations ofthe liquid drop 10, the electrodes may be arranged differently from therepresentation according to FIG. 2 so that for the correction of typicalimaging errors of the eye, deformations which are asymmetric in relationto the optical axis can be achieved and deformations can also beachieved in a controlled way locally as a function of the patient'svisual defect. A deliberate deformation of the interface 26 of theliquid lens 10 is thus achieved.

Various exemplary applications of liquid lens systems of the typedescribed above will be presented below.

FIG. 3 shows a so-called artificial eye, i.e. a device with the aid ofwhich the visual defect of the human eye can be replicated forexamination purposes etc. In FIG. 3, the radiation comes from the left.The first lens 30 is used to replicate the corneal curvature radius ofthe cornea of the eye. The radiation subsequently passes through a pupil32 whose aperture is adjustable, for example electrically ormechanically. The radiation then passes through a liquid lens system 34of the type described with the aid of FIGS. 1 and 2. The liquid lenssystem 34 thus makes it possible to adjust lens defects electrically byselectively applying different voltages U1, . . . , U8. With thedescribed optical system, the radiation is imaged onto an (artificial)retina 36, where it can be examined.

FIG. 4 shows a configuration of the artificial eye according to FIG. 3such that it is possible to obtain reproducible measurement results, inwhich for example temperature-induced changes in the surface tension ofthe liquid drop are compensated for. It is thereby also possible tobalance out control voltage fluctuations.

To this end, according to FIG. 4, a solid-state image camera 38 (forexample a CCD camera) is arranged behind the (artificial) retina whichis semitransparent for the radiation. The electrical image signalsobtained by the camera are processed in a computer 40. By the computer40, the pupil 32 and the liquid lens system 34 are driven in the mannerindicated by arrows.

A beam 44 of parallel light rays, which are generated for example by alaser beam and a matricial diaphragm, enters the artificial eye parallelfrom the left according to FIG. 4. For example, one hundred parallellight rays may form the beam 44. The image generated by the light raysin the region of the retina 36 in the camera 38 is represented by thereference numeral 42 in FIG. 4 (only 30 rays, for the sake ofsimplicity).

The positions of the individual light rays, as they are imaged by theartificial eye, are measured by the camera 38. The lens defect can bedetermined accurately from the position of the individual laser arrays.The measurement result is used either in order to assess the lens defector in order to determine a lens defect correction, by correctingdeviations from the expected lens defect via the said control voltagesU1 to U8. With the installed liquid lens system 34, the sphere and thecylinder of the artificial eye can be adjusted electrically.

The exemplary embodiment represented in FIGS. 3 and 4 may be expanded tothe extent that a plurality of liquid lens systems of the described typeare arranged successively staggered in the beam path, so that themeasurement range and the adjustment accuracy are increased.

FIG. 5 shows an application of liquid lens systems according to FIGS. 1and 2 in a so-called accommodation measuring instrument.

The measuring instrument according to FIG. 5 is constructed relativelysimply and makes it possible to measure the accommodation capacity of ahuman eye with high accuracy.

An object is imaged onto the retina of the eye 50 to be examined as animage via two liquid lens systems 52, 54. The display screen 56functions both as an object and as a target. A TFT display screen ispreferably employed as the display screen 56, or alternatively forexample a CRT display screen. No mechanically moving parts need to beused for the measurement. A computer 58 controls the two liquid lenssystems 52, 54 and the display screen 56. This arrangement particularlyadvantageously makes it possible for the brightness and the image sizeto be controlled with the display screen 56 so that the image formedcontains the same brightness and size irrespective of the visual defectof the eye being examined. A more accurate measurement of theaccommodation capacity is therefore possible. In order to measure theaccommodation capacity, for example, a sphere may be modified in themicrosecond range with the first liquid lens system 52 by applyingsuitable voltages U1, . . . , U8 by means of the computer 58. Thecylinder may be compensated for synchronously with the liquid lenssystem 54. The accommodation capacity of the eye 50 being examined canbe determined by changing the frequency of the generated imagemodification and examining the image formed on the retina by means ofthe display screen 56.

By adding further liquid lens systems or normal lenses to thearrangement according to FIG. 5, it is possible to increase themeasurement range as well as the measurement accuracy.

FIG. 6 shows an arrangement which can be used as a dioptric telescope,i.e. a measuring instrument for determining the dioptric value of an eyeto be examined. The block 60 in FIG. 6 is denoted as an accommodationmeasuring instrument with controllable lenses, i.e. the block 60 mayrepresent a system as described above with the aid of FIG. 5. With thearrangement according to FIG. 6, for example, an accommodation measuringinstrument 60 may be checked and calibrated.

According to FIG. 6, two liquid lens systems 62, 64 are arranged in thebeam path after the accommodation measuring instrument. The radiationthereby generated is imaged into a CCD camera 66. The image signals ofthe camera 66 are processed in a computer 68. In the manner indicated byarrows, the computer 68 controls the accommodation measuring instrument,the solid-state lens system 62 and the solid-state lens system 64, i.e.in the latter cases the adjustable voltages U1, . . . , U8 explainedabove.

With the said liquid lens systems, it is possible both to correct therefractive power and to compensate for the cylinder. Software in thecomputer 68 evaluates the digitally obtained image.

The arrangement according to FIG. 6 is small and compact. It isexclusively electrically controllable and allows straightforwardcalibration, so that the calibration also entails a time saving.Elaborate mechanics and optics can thus be obviated. The structureaccording to FIG. 6 also allows straightforward documentation of thecalibration process by means of the computer, and it allows objectivecalibration.

In order to calibrate the accommodation measuring instrument 60, adefined refractive power (for example −3 dpt) is adjusted with the firstliquid lens system 62 and a defined cylinder (for example 1 dpt 20°) isadjusted by means of the liquid lens system 64.

The refractive power and the cylinder are subsequently compensated forin the accommodation measuring instrument with the said controllablelenses. The camera 66 records an image and the computer 68 evaluatesthis image by means of image processing software. The image size must inthis case correspond to the setpoint image size, otherwise thecompensation in the accommodation measuring instrument must be continueduntil the image recorded by the camera 66 has reached the expected imagesize. The computer 68 also under-takes the control of the lenses in theaccommodation measuring instrument 60.

An accommodation measuring instrument may furthermore be checked withthe arrangement according to FIG. 6. To this end a defined refractivepower (for example −3 dpt) and a defined cylinder (for example 1 dpt20°) are adjusted in the accommodation measuring instrument. Thedioptric telescope according to FIG. 6 is then adjusted to the samerefractive power (for example −3 dpt) and the same cylinder (for example1 dpt 20°). If the accommodation measuring instrument is correctlycalibrated, then the image size of the image measured by the camera 66must coincide with the setpoint image.

The dioptric telescope according to FIG. 6 may be extended in itsmeasurement range by a combination of further liquid lens systems,optionally with glass or plastic lenses, and improved in respect of themeasurement accuracy by precompensation.

1. Artificial eye, characterised by a liquid lens system having a liquiddrop whose refractive property can be influenced by electrical fields; aplurality of electrodes which are arranged around the liquid drop; andan electrical voltage supply for selectively applying various voltagesto the electrode in order to generate different electrical fields, andhaving a further lens, which replicates a corneal curvature. 2.Artificial eye according to claim 1, having an adjustable pupil betweenthe lenses.
 3. Artificial eye according to claim 1, having a laser beamsource for generating a beam comprising a multiplicity of parallel lightrays, a CCD camera for recording images generated by the light raysafter they pass through the lenses, and having a computer for processingthe images and for controlling the liquid lens system as a function ofthe image processing.
 4. Measuring instrument for measuring theaccommodation of the eye, having a liquid lens system which comprisestwo liquid lenses that are respectively provided with a liquid dropwhose refractive property can be influenced by electrical fields; aplurality of electrodes which are arranged around the liquid drop; andan electrical voltage supply for selectively applying various voltagesto the electrode in order to generate different electrical fields, andhaving a computer for synchronously applying voltages to the electrodesof the liquid lenses.
 5. Measuring instrument according to claim 4,having a display screen for representing an image on the retina of theeye.
 6. Measuring instrument according to claim 5, having a computer forcontrolling the representation of an image so that the image size and/orthe brightness of the image on the display screen are independent of thevisual defect of the eye.
 7. Measuring instrument according to claim 4,wherein the computer drives one liquid lens system for a sphericalcorrection and the other liquid lens system for a cylinder correction.8. Artificial eye according to claim 2, having a laser beam source forgenerating a beam comprising a multiplicity of parallel light rays, aCCD camera for recording images generated by the light rays after theypass through the lenses, and having a computer for processing the imagesand for controlling the liquid lens system as a function of the imageprocessing.